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><H1
><A
NAME="VIDIOC-STREAMON"
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>ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN13821"
></A
><H2
>Name</H2
>VIDIOC_STREAMON, VIDIOC_STREAMOFF&nbsp;--&nbsp;Start or stop streaming I/O</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN13825"
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><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN13826"
></A
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int ioctl</CODE
>(int fd, int request, const int *argp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN13836"
></A
><H2
>Arguments</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="PARAMETER"
>fd</CODE
></DT
><DD
><P
>File descriptor returned by <A
HREF="r14090.htm"
><CODE
CLASS="FUNCTION"
>open()</CODE
></A
>.</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>request</CODE
></DT
><DD
><P
>VIDIOC_STREAMON, VIDIOC_STREAMOFF</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>argp</CODE
></DT
><DD
><P
></P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN13856"
></A
><H2
>Description</H2
><P
>The <CODE
CLASS="CONSTANT"
>VIDIOC_STREAMON</CODE
> and
<CODE
CLASS="CONSTANT"
>VIDIOC_STREAMOFF</CODE
> ioctl start and stop the capture
or output process during streaming (<A
HREF="x5791.htm"
>memory
mapping</A
> or <A
HREF="x5884.htm"
>user pointer</A
>) I/O.</P
><P
>Specifically the capture hardware is disabled and no input
buffers are filled (if there are any empty buffers in the incoming
queue) until <CODE
CLASS="CONSTANT"
>VIDIOC_STREAMON</CODE
> has been called.
Accordingly the output hardware is disabled, no video signal is
produced until <CODE
CLASS="CONSTANT"
>VIDIOC_STREAMON</CODE
> has been called.
The ioctl will succeed only when at least one output buffer is in the
incoming queue.</P
><P
>The <CODE
CLASS="CONSTANT"
>VIDIOC_STREAMOFF</CODE
> ioctl, apart of
aborting or finishing any DMA in progress, unlocks any user pointer
buffers locked in physical memory, and it removes all buffers from the
incoming and outgoing queues. That means all images captured but not
dequeued yet will be lost, likewise all images enqueued for output but
not transmitted yet. I/O returns to the same state as after calling
<A
HREF="r13696.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_REQBUFS</CODE
></A
> and can be restarted accordingly.</P
><P
>Both ioctls take a pointer to an integer, the desired buffer or
stream type. This is the same as struct&nbsp;<A
HREF="r13696.htm#V4L2-REQUESTBUFFERS"
>v4l2_requestbuffers</A
>
<CODE
CLASS="STRUCTFIELD"
>type</CODE
>.</P
><P
>Note applications can be preempted for unknown periods right
before or after the <CODE
CLASS="CONSTANT"
>VIDIOC_STREAMON</CODE
> or
<CODE
CLASS="CONSTANT"
>VIDIOC_STREAMOFF</CODE
> calls, there is no notion of
starting or stopping "now". Buffer timestamps can be used to
synchronize with other events.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN13876"
></A
><H2
>Return Value</H2
><P
>On success <SPAN
CLASS="RETURNVALUE"
>0</SPAN
> is returned, on error <SPAN
CLASS="RETURNVALUE"
>-1</SPAN
> and the <CODE
CLASS="VARNAME"
>errno</CODE
> variable is set appropriately:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><SPAN
CLASS="ERRORCODE"
>EINVAL</SPAN
></DT
><DD
><P
>Streaming I/O is not supported, the buffer
<CODE
CLASS="STRUCTFIELD"
>type</CODE
> is not supported, or no buffers have
been allocated (memory mapping) or enqueued (output) yet.</P
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